The invention relates to a halogen-free flame retardant and to a thermoplastic polymer composition, in particular a polymer composition on the basis of polyamides or polyesters, which is containing the halogen-free flame retardant. The thermoplastic polymer composition is particularly suitable for the production of polymer fibers in the melt spinning process.
For the production of flame retardant thermoplastic polymers, it is desirable for economic reasons to use nonreactive flame retardants since the latter can be introduced into a base polymer by a simple physical mixing or dissolution. In contracts thereto, the production of flame-retardant thermoplastic polymers using reactive flame retardants always requires at least one or more chemical process steps which are usually carried out already during the production of the base polymer.
For the production of flame-retardant thermoplastic polymers, it is desirable for economic reasons to use nonreactive flame retardants since the latter can be introduced into a base polymer by a simple physical mixing or dissolution. In contrast thereto, the production of flame-retardant thermoplastic polymers using reactive flame retardants always requires at least one or morel chemical process steps which are usually carried out already during the production of the base polymer.
Whereas nonreactive flame retardants allow a so-called “late addition” process in which the flame retardant is added to the base polymer only shortly before processing, usually during an extrusion process, it is normally not possible to use reactive flame retardants in a late addition process, since the latter react chemically with the base polymer and cause, in most causes, a polymer decomposition under the temperature and pressure conditions prevailing during extrusion.
For the production of polyamides finished to be flame-retarding, a large number of nonreactive flame retardants has already been in technical use for a long time. However, these are based in most cases on halogen- or antimony-containing substances which recently have come under public criticism due to their negative eco- and genotoxicological potential. For this reason, halogen- and antimony-free nonreactive flame retardants are increasingly used, such as, e.g., red phosphor, melamine polyphosphate, melamine cyanurate or aluminum phosphinates, as are described in EP-A 1 070 754, which in comparison with the substances containing halogen and antimony distinguish themselves by considerably better toxicological properties.
However, all aforementioned flame retardants are only partly suitable for use in melt spinning processes employed for the production of polyamide or polyester fibers. The halogenated flame retardants can considerably damage the spinning nozzles under the temperature and pressure conditions usual during spinning. In contrast thereto, melamine polyphosphate, melamine cyanurate or aluminum phosphinates are only insufficiently soluble in polyamides or polyesters which results in an inhomogeneous distribution of the flame retardant in the base polymer. This leads to considerable drawbacks in particular in the melt spinning process, since a clogging of the spinning nozzles is caused. In the case of red phosphor, merely intensively red dyed fiber products can be obtained, as known from document DE-A 21 48 348.
Document DE 26 46 218 A1 discloses phosphoric flame retardants which are obtained by addition reacting of 9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide (DOPO) to an unsaturated compound having at least one ester-forming functional group, and by a further reaction with an esterifying compound which is selected from dicarboxylic acids or esterifying derivatives thereof, diols or esterifying derivatives thereof, and oxycarboxylic acids or esterifying derivatives thereof. These phosphoric flame retardants are then reacted with dicarboxylic acids, such as terephthalic acid, and with a glycol so as to obtain flameproof polyesters.
Document DE 28 16 100 C2 discloses flame-retarding agents obtained by polycondensation of the addition product of DOPO or DOPO derivatives to itaconic acid with polyvalent alcohols, and having a molecular weight of from 1,000 to 20,000 g/mol and a phosphorous content of from 5.3 to 8.5% by weight.